1. Field of Invention
The embodiments of the present invention generally relate to a method and apparatus for supporting a web of polishing material in a polishing system.
2. Background of Invention
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to increase device density on a semiconductor workpiece, or substrate, such as a wafer. Chemical mechanical planarization systems generally utilize a polishing head to retain and press a substrate against a polishing material while providing motion therebetween. Some planarization systems utilize a polishing head that is moved over a stationary platen that supports the polishing material. Other systems utilize other motions, for example, providing a rotating platen. A polishing fluid is typically disposed between the substrate and the polishing material during polishing to provide chemical activity that assists in the removal of material from the substrate. Some polishing fluids also contain abrasives.
One type of polishing material that may be utilized for chemical mechanical polishing is known as fixed abrasive polishing material. Fixed abrasive polishing material generally comprises a plurality of abrasive particles suspended in a resin binder that is disposed in discrete elements on a backing sheet. As the abrasive particles are contained in the polishing material itself, systems utilizing fixed abrasive polishing materials generally utilize polishing fluids that do not contain abrasives.
FIG. 1 generally depicts a schematic of a conventional chemical mechanical polishing system 100 that utilizes a web 102 of polishing material to process a substrate 116. The polishing system 100 generally includes a polisher 104 having at least one polishing station 106. The polishing station 106 includes a platen 108 and a polishing head 110. The web 102 of polishing material is supported by the platen 108 below the polishing head 110. Generally, the platen 108 (or polishing table) has a top surface 112 that supports a polishing area 114 of the web 102 where processing occurs. The substrate 106 retained by the polishing head 110 is pressed against the polishing area 114 and moved relative thereto during processing.
The polishing area 114 of the web 102 is held against the platen 108 during processing typically by tensioning the web 102 between a supply roll 118 and a take-up roll 120 that are disposed on opposite sides of the platen 108. The top surface 112 of the platen 108 may additionally contain a groove 122 that circumscribes the polishing area 114. The groove 122 is coupled to a vacuum source 124 so that air and other fluids that may be present between the web 102 and the platen 108 are evacuated through the groove 122, thus pulling the web 102 flush against the top surface 112 of the platen 108.
A problem that is periodically encountered when using webs of polishing material is maintaining the web flush against the polishing surface. For example, the tension applied to the web between the supply roll and the take-up roll may cause the web to wrinkle along the direction of the web. As some polishing systems may tension the web in excess of 300 pounds, the disparity in the longitudinal and lateral stresses in the web creates a tendency of the web to wrinkle. Additionally, the web may creep across the platen during polishing due to the sheer forces experienced as the substrate is moved in relation to the web during polishing. As the web creeps, wrinkles are created. The wrinkles that are not be completely removed (i.e., flattened out) by the vacuum applied under the web create a non-planar surface that may disrupt polishing uniformity. Moreover, wrinkles extending across the vacuum sealing area at the edge of the platen may cause seal failure, thus allowing the web to separate from the platen.
Therefore, there is a need for a method and apparatus that improves the retention of polishing material in a polishing station.
In one aspect of the invention, an apparatus for retaining a web of polishing material is provided. In one embodiment, an apparatus for retaining a web of polishing material includes a platen that has a first clamp and a second clamp disposed on opposite sides of the platen. A top surface of the platen is adapted to support the web of polishing material in an orientation having the web""s edges disposed approximate the first and second sides of the platen. The first and second clamps are actuated to laterally tension the web therebetween.
In another aspect of the invention, a method for retaining a web of polishing material to a platen is provided. In one embodiment, the method includes the steps of disposing a web of polishing material on a platen and laterally tensioning the web.